In a mobile communication system, communication quality in radio communications greatly influences transmission characteristics and quality of service. To improve the transmission characteristics and to maintain sufficient quality of service, network operators evaluate communication quality in their communication areas and try to improve the communication quality by adjusting various parameters. Here, “communication quality” is represented, for example, by a delay profile or a received signal-to-interference ratio (SIR).
For a CDMA-based mobile communication system, Japanese Patent Application Publication No. 11-193699, for example, discloses a service area evaluation system and a method and an apparatus for obtaining service area evaluation data used for evaluation of communication quality in a communication area. In CDMA, generally, dedicated channels are used for communications and transmission power control is used for link adaptation, a technology for adapting to fluctuations in reception levels such as Rayleigh fading and shadow fading.
Meanwhile, a successor communication system to W-CDMA, i.e., Long Term Evolution (LTE), is currently being discussed by 3GPP, a standardization group for W-CDMA. In LTE, orthogonal frequency division multiplexing (OFDM) is to be used as a downlink radio access method and single-carrier frequency division multiple access (SC-FDMA) is to be used as an uplink radio access method (see, for example, 3GPP TR 25.814 (V7.0.0), “Physical Layer Aspects for Evolved UTRA,” June 2006).
OFDM is a multi-carrier transmission method where a frequency band is divided into multiple narrow frequency bands (subcarriers) and data are transmitted on the subcarriers. The subcarriers are densely arranged along the frequency axis such that they partly overlap each other but do not interfere with each other. This method enables high-speed transmission and improves frequency efficiency.
SC-FDMA is a single-carrier transmission method where a frequency band is divided into multiple frequency bands and the frequency bands are allocated to different terminals for transmission in order to reduce interference between the terminals. Also, SC-FDMA reduces variation of the transmission power and therefore makes it possible to reduce power consumption of terminals and to achieve wide coverage.
In a mobile communication system based on LTE, shared channels are used for both uplink and downlink, and adaptive modulation and coding (AMC) is used for link adaptation.